Scheduling and link adaptation in wireless telecommunications systems

ABSTRACT

The invention relates to control of link resources in a wireless telecommunications system, in which instant channel feedback information is transmitted from a mobile terminal in response to receipt of a selection message from a basestation, and the instant channel feedback information is used for real-time resource allocation and adaptation at the basestation.

The present invention relates to wireless telecommunications systems,and, in particular, to 3G telecommunications networks.

BACKGROUND OF THE PRESENT INVENTION

An exemplary wireless telecommunications system 1 is illustrated in FIG.1 of the accompanying drawings, and includes a number of basestations 10a, 10 b and 10 c, which communicate over a radio frequency (RF) airinterface with mobile terminals 20 a, 20 b, 20 c, 20 d, and 20 e. Themobile terminals are sometimes referred to as “user equipment (UE)”. Itwill be appreciated that the number of basestations and mobile terminalsis merely exemplary, and that the systems can include any appropriatenumber of such units.

In order for communication, that is, data transfer, to be successfulbetween the basestations 10 and the mobile terminals 20, communicationschannels are allocated to respective mobile terminals. These channels,or “links”, can be allocated in the time domain and/or the frequencydomain, as is well known. Communications from a basestation 10 to amobile terminal 20 are known as downlink communications, andcommunications from the mobile terminal 20 to the basestation 10 areknown as uplink communications. The communications channels allocatedfor such data transfer are know as the downlink (DL) and the uplink (UL)respectively.

In order to increase capacity and coverage, some wirelesstelecommunications systems make use of link adaptation and scheduling.In order to support such techniques, feedback information, such aschannel state information (CSI) or channel quality indicator (CQI)information is required. Such feedback information has to be suppliedfrequently and accurately so that the allocated communication channelsin the system can be maintained at the appropriate quality level. As isknown, transmission mode adaptation and link adaptation are terms usedin wireless communications to denote the matching of the modulation,coding and other signal and protocol parameters to the conditions on theradio link (for example, the interference due signals coming from othertransmitters, the sensitivity of the receiver, the available transmitterpower margin, etc.). The process of link adaptation is a dynamic one andthe signal and protocol parameters can change as the radio linkconditions change.

For a wideband wireless system that supports a large number of mobileterminals, the bandwidth required for the signalling of CSI/CQI andother feedback information is very high, and represents a verysignificant burden on the uplink. Although this is true for bothtime-domain, and for time and frequency domain systems, it is the timeand frequency domain system that suffers most, since the total resourceis cut to much finer granularity and a higher number of CSI/CQI signalsare required due to more small-size sub-units.

3GPP™ Release 5 (Third Generation Partnership Project) introduces theconcepts of link adaptation and scheduling in HSDPA (High-Speed DownlinkPacket Access) systems. The resource allocation and transport format andresource related information (TFRI) is carried by the High Speed SharedControl Channel (HS-SCCH). The HS-SCCH is two time slots ahead of thedata transmission and is carried over the High Speed Downlink SharedChannel (HS-DSCH). Accordingly, scheduling and link adaptation iscarried out at the same time, two time slots ahead of the datatransmission. Every mobile terminal in the system performs channelquality reporting at regular intervals, so that such signalling istransmitted for each channel in the system on a continual basis.

It will, therefore, be appreciated that use of link adaptation andscheduling in wideband wireless telecommunications systems is desirablein order to increase capacity of the systems, but has the significantproblem that channel quality reporting by the mobile terminals uses anundesirably high proportion of the available uplink bandwidth.

Accordingly, it is desirable to provide a technique that enables linkadaptation and scheduling in a wideband wireless telecommunicationssystem, and which reduces the amount of channel quality reportingrequired from the mobile terminals.

SUMMARY OF THE PRESENT INVENTION

Embodiments of the present invention provide techniques for reducing theamount of feedback information signalling required for scheduling andtransmission mode adaptation in a wireless telecommunications system.Such reduction is achieved by selecting only a subset of all the mobileterminals that communicate with a basestation for scheduling, linkadaptation and other transmission mode adaptation at one time.

According to one aspect of the present invention, there is provided amethod of controlling downlink resources in a wirelesstelecommunications system, the link resources being provided by abasestation of the system for enabling communication from thebasestation to a plurality of mobile terminals, the method comprisingselecting a subset of mobile terminals from the plurality of mobileterminals communicating with the basestation, obtaining feedbackinformation from the mobile terminals in the selected subset, suchfeedback information being supplied in response to such selection,performing transmission mode adaptation for the mobile terminals in theselected subset in dependence upon the obtained feedback information.

According to another aspect of the present invention, there is provideda method of receiving data at a mobile terminal of a wirelesstelecommunications system from a basestation, the method comprisingreceiving a selection message from a basestation, transmitting feedbackinformation to the basestation in response to receipt of the selectionmessage therefrom, and receiving data from the basestation.

According to another aspect of the present invention, there is provideda basestation for use in a wireless telecommunications system, thebasestation comprising a controller operable to select a subset ofmobile terminals from a plurality of mobile terminals communicating withthe basestation, a receiver operable to obtain feedback information frommobile terminals in the selected subset, such feedback information beingsupplied in response to such selection, a resource allocation unitoperable to perform transmission mode adaptation for the mobileterminals in the selected subset in dependence upon obtained feedbackinformation.

According to yet another aspect of the present invention, there isprovided a mobile terminal for use in a wireless telecommunicationssystem, the mobile terminal comprising a receiver for receiving aselection message, a feedback generation unit operable to generatefeedback information, and a transmitter for transmitting feedbackinformation to a basestation in response to reception of a selectionmessage therefrom, the receiver also being operable to receive data overan allocated wireless link.

According to yet another aspect of the present invention, there isprovided a method of controlling uplink resources in a wirelesstelecommunications system, the uplink resources being provided by abasestation of the system for enabling communication from a plurality ofmobile terminals and the basestation, the method comprising receivingrespective transmission request messages from a plurality of mobileterminals, selecting a subset of mobile terminals from the plurality ofmobile terminals for UL pilot transmission, obtaining channelinformation relating to the mobile terminals in the selected subset,performing transmission mode adaptation for the mobile terminals in theselected subset in dependence upon the obtained feedback information.

According to yet another aspect of the present invention, there isprovided a basestation for use in a wireless telecommunications system,the basestation comprising a receiver operable to receive respectivetransmission request messages from a plurality of mobile terminals, acontroller operable to select a subset of mobile terminals from theplurality of mobile terminals, and to obtain channel informationrelating to the mobile terminals in the selected subset, and to performtransmission mode adaptation for the mobile terminals in the selectedsubset in dependence upon the obtained feedback information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cellular wireless telecommunications system;

FIG. 2 is a simplified block diagram of a basestation for use in awireless telecommunications system;

FIG. 3 is a simplified block diagram of a mobile terminal for use in awireless telecommunications system;

FIG. 4 illustrates steps carried out by a basestation in a methodembodying the present invention for use in controlling downlinkresources; and

FIG. 5 illustrates steps carried out by a mobile terminal in the methodembodying the present invention relating to downlink resources.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Techniques embodying the present invention are applicable to wirelesstelecommunications systems such as that illustrated in FIG. 1. Asdescribed above, the exemplary system of FIG. 1 includes a number ofbasestations 10 a, 10 b and 10 c, which communicate over a radiofrequency (RF) air interface with mobile terminals 20 a, 20 b, 20 c, 20d, and 20 e.

A simplified block diagram of a basestation for use in accordance withtechniques embodying the present invention is shown in FIG. 2. Thebasestation 10 includes a controller 101, which itself includes aresource allocation unit 103. The basestation 10 also includestransmitter (TX) and receiver (RX) circuitry for transmitting andreceiving radio frequency signals to and from an antenna 109respectively. The antenna provides the wireless communication path withthe mobile terminals. The controller 101 communicates data with thetransmitter 105 and the receiver 107. The controller is also incommunication with the operator network (not shown). Operation of theresource allocation unit will be described in detail below. However, itwill be readily appreciated that the function of the resource allocationunit could be provided outside of the controller 101 of the basestation10. For example, the resource allocation unit could be providedcentrally in the operator network. The resource allocation unit is shownas part of the basestation for the sake of clarity.

FIG. 3 illustrates a simplified block diagram of a mobile terminal foruse in accordance with the techniques embodying the present invention.The mobile terminal 20 includes a controller 201, a man machineinterface 205, transmitter and receiver circuitry 207 and 209, and anantenna 211. As is well known and understood, the controller 201 of themobile terminal 20 controls data communications with a basestation of awireless telecommunications system via the transmitter 207, the receiver209 and the antenna 211. A user interacts with the mobile terminal byway of the man machine interface (MMI) 205, which may include suchdevices as a display screen, a keypad, a microphone, and a loudspeaker.

The controller 201 of the mobile terminal 20 includes a feedbackmeasurement unit 203 which operates to generate feedback informationrelating to link resources to which the mobile terminal has access. Thefeedback information can be channel state information (CSI), channelquality indicator (CQI), multi-antenna transmission weights, beamselection indicator or any appropriate measure.

A method embodying the present invention, which relates to control ofdownlink resources, will now be described with reference to the flowcharts of FIGS. 4 and 5, as well as to the block diagrams of FIGS. 2 and3. The method will be described in detail with reference to downlinkcommunications from the basestation 10 to the mobile terminals 20, andwill assume that each mobile terminal makes use of a single channel andservice. It will be readily appreciated that the techniques can beapplied to a multi-channel, multi-service environment.

At step 4A, the resource allocation unit 103 selects a subset of themobile terminals communicating with the basestation 10. This selectionis made so as to reduce the number of mobile terminals requiringscheduling and transmission adaptation at any one time. The mobileterminals are preferably selected from those which are actively waitingin a packet data mode for reception of data packets.

Selection of the subset of mobile terminals can be made by evaluatingany appropriate criteria. In a channel dependent scheduling andadaptation scheme, if no channel feedback information is available, thenchannel independent information can be used to make the selection of thesubset of the mobile terminals. For example, packet data unit (PDU)size, discontinuous transmission (DTX) time, block error rate (BLER)requirement, delay requirement, and/or jitter requirement may be used todetermine the mobile terminals to be selected as part of the subset. Inaddition, or alternatively, buffer sizes of the transmitter, thepriority of a mobile terminal's service, prediction of a mobileterminal's handover likelihood, and/or data rate requirement may be usedin the selection of mobile terminals.

When some feedback information is available, for example a CQI feedbackwith a long time period, the respective priorities of the mobileterminals are preferably used to determine the selection. The factorsmentioned above may also be considered when selecting the mobileterminals.

In the case of channel-independent scheduling, the selected subset ofmobile terminals can be determined by random selection using a seedsignal broadcasted in the common control channel.

The resource allocation unit 103 may now allocate link resources to eachof the selected mobile terminals (step 4B). In time domain systems, thismeans that respective time slots are allocated to the selected subset ofmobile terminals for transmission of data thereto.

In time and frequency domain systems, the time-frequency combinationsare divided into time-frequency resource blocks, and respective resourceblocks are allocated to each of the mobile terminals in the selectedsubset of mobile terminals. This block allocation can also includedetermination of power allocations and/or transmit weights for theselected subset of mobile terminals.

Instead of allocating specific link resources to each of the selectedmobile terminals, the link allocation unit 103 may pre-allocate a rangeof link resources to be allocated later to specific mobile terminals.

Alternatively, no link resource allocation may be performed at thisstage, in which case the method moves directly from step 4A to step 4C

At step 4C, the selected mobile terminals are informed of theirselection by the transmission of respective selection messages from thebasestation 10 to the mobile terminals 20 concerned via the basestationtransmitter 105 and antenna 109. Each selection message can also includeinformation regarding the type of feedback information that is requiredfrom the mobile terminal 20. The options for the variations in type offeedback information will be discussed below. Alternatively, a commonselection message can be sent to the mobile terminals 20, in whichcommon message the selected mobile terminals are identified.

A selected mobile terminal 20 receives the selection message (step 5A)via the antenna 211, and the receiver 209, and, in response to itsreception, generates and transmits feedback information (step 5B) to thebasestation.

Receipt of the selection message by a mobile terminal causes the mobileterminal 20 to transmit feedback information, such as CSI, CQI or beamselection indicator, to the basestation 10. In the case where theresource allocation unit 103 has allocated specific link resources tothe mobile station, the feedback information relates to those specificresources. In the case where the basestation merely pre-allocates arange of resources to the selected subset of mobile terminals, then thefeedback information from each selected mobile terminal relates to thewhole range of the pre-allocated resources, for example to an averagefeedback signal from the range. When no resources are specificallyallocated to the mobile terminals before issuance of the selectionmessage, then the feedback information relates to the whole of theavailable resource band.

The feedback information is received from each mobile terminal of theselected subset of mobile terminals 20 by the basestation 10 (step 4D),via the antenna 109, and receiver 107. The controller 101, and theresource allocation unit 103 then use the received feedback informationto enable scheduling, link adaptation and other required transmit modeadaptation to be performed for the selected subset of mobile terminals20 (step 4E). The actual amount of scheduling that needs to be performedat this stage is dependent upon the amount performed immediately afterthe selection of the mobile terminals in step 4 a. If resources arefully allocated in step 4B, then no further scheduling is needed.Naturally, however, if scheduling at step 4B was not complete, thencompletion of the scheduling is needed at step 4E.

Transmission adaptation can include choosing transmission mode. Forexample, selection of transmission mode can include selecting modulationmodes and coding rates, and/or selecting one or more modes from a groupincluding a multi-antenna mode, a single stream mode, a multi-streammode, and a beam-forming mode.

In addition, performing transmission adaptation may include allocatingtransmission power, transmission weights, and/or beams.

Following scheduling and transmission mode adaptation, data aretransmitted (step 4F) from the basestation to the selected subset ofmobile terminals using the allocated resources. The mobile terminalsthen receive the transmitted data (step 5C).

As mentioned above, the selection message sent to a mobile terminal 20may include information defining the type of feedback information thatis to be returned to the basestation. For example, either block level orframe level feedback information can be specified. As is known, framelevel feedback occurs less frequently than block level feedback.

For the mobile terminals with high mobility, frame level feedbackinformation should preferably be chosen. For mobile terminals located ata cell edge that therefore cannot support a high enough bit rate forblock-wise feedback, should also make use of frame level feedbackinformation, if the resource allocation unit makes an allocation ofresources to the mobile terminals following selection of the subset,then frame level feedback can be used in order to reduce further thefeedback overhead.

For frame level feedback, the feedback information can be averagedacross the selected mobile terminals which are to make use of framelevel feedback. Accordingly, only a single feedback informationtransmission is required per user per frame. This greatly reduces theamount of feedback information being transmitted to the basestation.

If frequency-domain scheduling and adaptation is to be performed, thenit is necessary to request block level feedback information from theselected mobile terminals. For example, if PFTF scheduling or block-wiseprecoding or beamforming is to be used, then block level feedbackinformation is required.

By selecting a subset of the mobile terminals, the amount of feedbackinformation being transmitted to the basestation is reduced from theamount in which mobile terminals continually transmit feedbackinformation according to a predetermined schedule. In embodiments of thepresent invention, feedback information is only required from selectedmobile terminals. In addition, determining the appropriate type offeedback information feedback mechanism allows the system to reducefurther the amount of feedback information being transmitted.

It will be appreciated that the feedback information used for linkadaptation and other transmit mode adaptations in embodiments of thepresent invention can be provided by any quality measure appropriate forthe radio link concerned. For example, channel state information (CSI),channel quality indicator information (CQI), transmission weights orbeam selection indicator can be utilised.

The techniques described with reference to downlink data transmissionare applicable to uplink transmissions, albeit with some differences, asdescribed below.

The basestation 10 still makes the selection decision regarding themobile terminals, following receipt of respective transmission requestsfrom the mobile terminals. The selection message includes informationregarding which mobile terminals should transmit its pilot transmissionsignal and probably the additional information of the bands for pilottransmissions. The basestation receives the pilot signals, and thengenerates channel information equivalent to the feedback informationdiscussed above. The control 101 and the resource allocation unit 103use this channel information to schedule the transmissions, and toprovide transmission adaptation information to the mobile terminals.

The techniques described above enable a wideband wirelesstelecommunications system to reduce the amount of bandwidth required inthe uplink for transmission of feedback information from the mobileterminals to the basestation, whilst maintaining desirably high qualityof timely feedback information. This high quality feedback informationenables high quality transmission adaptation to be performed, therebyenabling high quality communications between the basestation and mobileterminals. The techniques are applicable to any system in which commonresources are shared by mobile terminals. For example, multi-carrierCDMA systems, OFDMA systems, or HSDPA systems, can all benefit from thetechniques embodying the present invention.

1.-53. (canceled)
 54. A method of controlling downlink resources in awireless telecommunications system, the link resources being provided bya basestation of the system for enabling communication from thebasestation to a plurality of mobile terminals, the method comprising:selecting a subset of mobile terminals from the plurality of mobileterminals communicating with the basestation; pre-allocating linkresources to the mobile terminals in the selected subset of mobileterminals; sending a selection message to the mobile terminals in theselected subset of mobile terminals with a requirement for feedbackinformation; obtaining feedback information from the mobile terminals inthe selected subset; performing transmission mode adaptation for themobile terminals in the selected subset in dependence upon the obtainedfeedback information.
 55. A method as claimed in claim 54, wherein themobile terminals in the plurality of mobile terminals are activelywaiting in a packet data reception mode.
 56. A method as claimed inclaim 54, comprising the further step of, transmitting data to themobile terminals of the subset by applying the transmission modes asadapted.
 57. A method as claimed in claim 54, wherein selection of thesubset of mobile terminals is made in dependence upon predeterminedselection criteria.
 58. A method as claimed in claim 57, wherein thepredetermined criteria include service characteristics, transmitterbuffer size, transmission priority, and handover prediction.
 59. Amethod as claimed in claim 54, wherein selecting a transmission modeincludes selecting modulation modes and coding rates.
 60. A method asclaimed in claim 59, wherein selecting a transmission mode includesselecting one or more modes from a group including a multi-antenna mode,a single stream mode, a multi-stream mode, and a beam-forming mode. 61.A method as claimed in claim 54, wherein performing transmission modeadaptation includes allocating transmission power for the selectedmobile terminals.
 62. A method as claimed in claim 54, whereinperforming transmission mode adaptation includes allocating transmissionweights, or beams.
 63. A method as claimed in claim 54, wherein thefeedback information is obtained in distinct, time-separated, portions.64. A method as claimed in claim 63, wherein the distinct, timeseparated, portions relate to respective quality parameters.
 65. Abasestation for use in a wireless telecommunications system, thebasestation comprising: a controller operable to select a subset ofmobile terminals from a plurality of mobile terminals communicating withthe basestation; a resource allocation unit is operable to pre-allocatelink resources to the mobile terminals in the selected subset of mobileterminals; the resource allocation unit is further operable to send aselection message to the mobile terminals in the selected subset ofmobile terminals with a requirement for feedback information; a receiveroperable to obtain feedback information from mobile terminals in theselected subset; the resource allocation unit operable to performtransmission mode adaptation for the mobile terminals in the selectedsubset in dependence upon obtained feedback information.
 66. Abasestation as claimed in claim 65, wherein the controller is operableto select mobile terminals from a plurality of mobile that are activelywaiting in a packet data reception mode.
 67. A basestation as claimed inclaim 65, wherein the resource allocation unit is further operable tocontrol data is transmitted to the mobile terminals of the subset byapplying the transmission modes as adapted.
 68. A basestation as claimedin claim 65, wherein selection of the subset of mobile terminals is madein dependence upon predetermined selection criteria.
 69. A basestationas claimed in claim 68, wherein the predetermined criteria includeservice characteristics, transmitter buffer size, transmission priority,and handover prediction.
 70. A basestation as claimed in claim 65,wherein transmission mode adaptation includes selecting a transmissionmode for selected mobile terminals.
 71. A basestation as claimed inclaim 70, wherein selecting a transmission mode includes selectingmodulation modes and coding rates.
 72. A basestation as claimed in claim65, wherein selecting a transmission mode includes selecting one or moremodes from a group including a multi-antenna mode, a single stream mode,a multi-stream mode, and a beam-forming mode.
 73. A basestation asclaimed in claim 65, wherein transmission mode adaptation includesallocating transmission power for selected mobile terminals.
 74. Abasestation as claimed in claim 65, wherein transmission mode adaptationincludes allocating transmission weights, or beams.
 75. A basestation asclaimed in claim 65, wherein the feedback information is obtained indistinct, time-separated, portions.
 76. A basestation as claimed inclaim 75, wherein the distinct, time separated, portions relate torespective quality parameters.
 77. A method of controlling uplinkresources in a wireless telecommunications system, the uplink resourcesbeing provided by a basestation of the system for enabling communicationfrom a plurality of mobile terminals and the basestation, the methodcomprising: receiving respective transmission request messages from aplurality of mobile terminals; selecting a subset of mobile terminalsfrom the plurality of mobile terminals; pre-allocating link resources tothe mobile terminals in the selected subset of mobile terminals; sendinga selection message to the mobile terminals in the selected subset ofmobile terminals with a requirement for feedback information; obtainingchannel information relating to the mobile terminals in the selectedsubset; performing transmission mode adaptation for the mobile terminalsin the selected subset in dependence upon the obtained feedbackinformation; transmitting transmission mode adaptation information tothe mobile terminals in the selected subset.
 78. A method as claimed inclaim 77, wherein the channel information is based upon pilot signalsreceived by the mobile terminals in the selected subset of mobileterminals.
 79. A method as claimed in claim 77, comprising performingresource allocation in dependence upon the obtained channel information.80. A method as claimed in claim 77, wherein selection of the subset ofmobile terminals is made in dependence upon predetermined selectioncriteria.
 81. A method as claimed in claim 80, wherein the predeterminedcriteria include service characteristics, transmitter buffer size,transmission priority, and handover prediction.
 82. A method as claimedin claim 77, wherein performing transmission mode adaptation includesselecting a transmission mode for the selected mobile terminals.
 83. Amethod as claimed in claim 82, wherein selecting a transmission modeincludes selecting modulation modes and coding rates.
 84. A method asclaimed in claim 82, wherein selecting a transmission mode includesselecting one or more modes from a group including a multi-antenna mode,a single stream mode, a multi-stream mode, and a beam-forming mode. 85.A basestation for use in a wireless telecommunications system, thebasestation comprising: a receiver operable to receive respectivetransmission request messages from a plurality of mobile terminals; acontroller operable to select a subset of mobile terminals from theplurality of mobile terminals; a resource allocation unit is operable topre-allocate link resources to the mobile terminals in the selectedsubset of mobile terminals; the resource allocation unit is furtheroperable to send a selection message to the mobile terminals in theselected subset of mobile terminals with a requirement for feedbackinformation; a receiver operable to obtain channel information frommobile terminals in the selected subset; the resource allocation unitoperable to perform transmission mode adaptation for the mobileterminals in the selected subset in dependence upon obtained feedbackinformation.